1. Field of the Invention
This invention relates to a lens barrel using a vibration wave motor as a drive source.
2. Related Background Art
Numerous lens barrels having incorporated therein a motor for the focusing and magnification changing operations of a focus lens or a zoom lens and effecting the driving of the motor by an electrical signal from focus detecting means or zoom control means are known. The motors incorporated in the prior-art lens barrels are iron core motors, coreless motors or brushless motors in which a coil is wound on an iron core and a rotary shaft is fixed to the iron core, so-called solid type motors in which a rotary shaft is fixed to a permanent magnet and a coil without an iron core is wound around the permanent magnet, or hollow type motors according to the applicants previous patent application (U.S. Application Ser. No. 688,365) in which the rotor portion and stator portion of a motor are of a hollow structure. Further, stepping motors are also known as motors of a hollow structure.
The above-mentioned conventionally used solid type motors and hollow type motors are of a structure utilizing a rotational movement based on an electromagnetic action and suffer from various problems in the rotation of the rotor.
One of the problems is that there are vibrations during the rotation of the rotor and in the case of a lens barrel for a single lens reflex camera or a lens barrel for a lens or shutter camera, those vibrations cause the camera to assume vibrations of the camera which in turn cause out-of-focus state.
Also, these vibrations involve vibration noise which diminishes the photographer's pleasure in taking pictures.
Further, the aforementioned electromagnetic motors require a reduction gear train for controlling the rotational speed and rotational torque of the rotor, and the incorporation of the reduction gear train into the lens barrel results in the complicated structure of the lens barrel, an increased number of parts and a complicated process of assembly, which in turn greatly affects the cost.